Thanks for clarifying, I figured fashion had at least something to do with it given the number of actively used protocols and services that still use it, XMPP being the one I use the most myself.

Even on XMPP I have seen several projects to "translate" the protocol into other languages (specifically Rust in one).

Efficiency makes sense, but then also the number of devs proficient in a language due to shifts in the emphasis of training and education is just as strong a force.